1. Field
The present invention relates to ceramic honeycomb articles, and more particularly to porous cordierite ceramic honeycomb articles and methods for manufacturing same.
2. Technical Background
Recently, much interest has been directed towards the diesel engine due to its fuel efficiency, durability, and economical aspects. However, diesel emissions have been scrutinized both in the United States and Europe. As such, stricter environmental regulations will likely require diesel engines to be held to relatively high standards in terms of filtration efficiency. Therefore, diesel engine manufacturers and emission-control companies are working to achieve diesel engine emission control methods and apparatus which will meet such stringent emission requirements.
One of the biggest challenges in lowering diesel emissions is controlling the levels of diesel particulate material (PM) present in the diesel exhaust stream. Diesel particulate material consists mainly of carbon soot. The currently favored approach for removing carbon soot from diesel exhaust is through the use of diesel traps (otherwise referred to as “wall-flow filters” or “diesel particulate filters”). Diesel particulate filters capture soot in the diesel exhaust on and in the porous ceramic walls of the filter body. Diesel filters are described in, for example, U.S. Pat. Nos. 4,329,162, 4,415,344, 4,416,676, 4,417,908, 4,420,316, and 4,455,180. A design goal for diesel particulate filters is to provide for excellent filtration of soot without significantly hindering the exhaust flow, i.e., via providing relatively low back pressure. However, meeting both these goals simultaneously has proven very elusive. Additionally, as the layer of soot collects in the inlet channels and walls of the diesel particulate filter, the accumulating soot layer causes a gradual rise in the back pressure of the filter against the engine, thereby causing the engine to work harder. Thus, once the soot in the filter has accumulated to some level, the filter must be regenerated by burning out the soot, to restoring the back pressure again to low levels. Normally, this regeneration is accomplished under actively controlled conditions of engine management whereby a slow burn is initiated which lasts for a number of minutes, during which the temperature in the filter rises from a lower operational temperature to a maximum temperature. This burnout cycle has been referred to in the industry as an “active regeneration.” Minimizing such events is preferred to maximize durability of the filter as well as to minimize fuel penalties. Further, minimizing peak temperatures during such events is desirable. Thus, filter configurations which may minimize regeneration events or reduce peak temperatures are sought after.
Cordierite, being a low-cost material, has been one material utilized for diesel exhaust filtration. To that end, porous cordierite ceramic filters of the wall-flow type have been utilized for the removal of particles in the exhaust stream from some diesel engines. A diesel particulate filter (DPF) ideally should combine low CTE (for thermal shock resistance), low pressure drop (for fuel efficiency), and high filtration efficiency (for a high level of removal of particles from the exhaust stream). Additionally, such filters should have high strength (to survive handling, canning, and vibration in use, for example). However, achieving this combination of features has proven very elusive with current state-of-the-art cordierite DPFs.
Thus, it would be considered a significant advancement to obtain a porous ceramic honeycomb article, made of cordierite, which exhibits high filtration efficiency coupled with low pressure drop.